Centrifugal pumps



Oct. 26, 1965 K. D. MGMAHAN 3,213,797

CENTRIFUGAL PUMPS Original Filed Feb. 12, 1963 3 Sheets-Sheet 1 INVENTOR KENTON D. MC MA HAN F|G.|.

BW m

ATTORNEY j Y Oct. 26, 1965 K. D. M MAHAN 3,213,797

CENTRIFUGAL PUMPS Original Filed Feb. 12, 1965 3 Sheets-Sheet 2,

[III/III,

INVENTOR KENTON MC MAHAN ATTORNEY v F I G, 3 a

Oct. 26, 1965 K. D. M MAHAN CENTRIFUGAL PUMPS 3 Sheets-Sheet 3 Original Filed Feb. 12, 1963 3 F I G. 5.

INVENTOR KENTON D.MCMAHAN JQ'M TOR NEY United States Patent 11 Claims. Cl. 103-87) The present invention relates to centrifugal fluid pumps and more particularly to multi-stage centrifugal pumps, and the present application is a division of my application Serial No. 258,033, filed February 12, 1963. The basic concept of the reduction of interstage losses in multistage centrifugal machines by the use of a plurality of radial jets of balanced momentum is the same as that disclosed in US. Patent No. 2,868,440 and co-pending application Serial No. 175,940, now US. Patent No. 3,171,353.

In Patent 2,868,440, it was disclosed that if two jets of equal magnitude (jet velocityx mass) created from the discharge of an impeller of an earlier stage unit are directed in opposed directions radially inwardly towards the suction eye in alignment along a radial center plane and in centered position over the axis of the eye, substantially balanced impact of the two jets is effected as they meet in the vicinity of said suction eye and substantially smooth axial deflection of said jets into said suction eye is effected as they merge into a single stream. By creating diametrically opposed jets of equal magnitude from each impeller discharge, the rotational velocity components, turbulences, undesired accelerations, eddies and vacuous pockets in the stream flow between the discharge of a volute of one stage and the intake or eye of a succeeding stage, resulting in so called interstage losses, and consequent lowering of overall performance and efficiency of multi-stage machines, are materially reduced.

In copending application Serial No. 175,940, it has been disclosed that the radial jets from the discharge of the volutes need not be diametrically opposed to suppress the rotational components and other undesirable effects in the said jets, but that these factors disturbing the efliciency of centrifugal machines can be materially reduced if the magnitude of the radial jets and the spacing therebetween is such that the resultant of the radial momentum (jet velocityxmass) on one side of any selected radial plane passing through the axis of the inlet suction eye is substantially equal to and in substantial radial alignment with the resultant of the radial jet momentum on the other side of the plane. In accordance with this disclosed concept, an odd number of radial jet passages properly spaced will provide the desired jet balance to reduce interstage losses. It was further disclosed that the tendency of the jets from the perimetric volutes of one stage when turned radially inward by a conventional elbow to crowd toward the outer bend and away from the inner bend of said elbow, can be compensated for by the use of overbends or overextended bends, whereby a single radial jet of very nearly uniform velocity, mass and direction thereacross and with the resultant of its momentum almost coextensive in position with the radial mechanical centerline of the jet, is produced without the use of inner vanes and the like. Also, by this means, the circumferential spaced confining walls on the circumferential spaced boundaries of the radial jet passages are eliminated. As a result, the radial jets of one stage enter the eye of the next stage with little or no rotational components and without measurable loss.

The present invention contemplates the use of modern transistorized frequency changing power pacts which permit the operation of high frequency induction motors on standard 60-cycle alternating current power sources at any desired design speed, and thus makes the pump, in

3,213,797 Patented Oct. 26, 1965 accordance with the present invention applicable to submersible deep well pumps as well as many other and varied applications. The availability of any desired design speed on a standard power source without the need for brushes, permits the most efficient and least expensive design of pump to cover a Wide range of well depths and How requirements in the same overall sized pump.

One object of the present inveniton is to provide a new and improved multi-stage pump for liquids of zero or low compressibility and especially containing absorbed or mixed air, gases or vapors, which pump is designed for operation at relatively high speeds with a minimum of interstage losses and high overall performance and efliciency, and which at the same time is capable of being manufactured at much lower cost than conventional submersible pumps.

Another object of the pr'esent invention is to provide a new and improved centrifugal liquid pump having means for separating mixed or absorbed air or gases within the pumped liquid and for expelling the separated air or gases from the eyes of the impellers and the pumped liquid system.

To attain the latter object of the invention, a small venturi type injector pump provided in the center of the rotating shaft has vent holes at the venturi throat communicating with the respective eyes of the impellers to remove the separated air or gasbubbles or pockets by aspiration. A very small percentage of the liquid discharged from the last stage acting as the aspirating liquid operates the injector.

It is well known that most commonly pumped liquids such as water, fuel oils etc. contain a substantial percentage of absorbed air or in the case of oils may contain air bubbles in the form of foam. When such liquids are agitated at slightly reduced pressure, such as exists at the eye of a high speed impeller, the absorbed air is centrifuged out and collects at the hub or shaft and builds up, until the entire entrance to the impeller is blocked and the pump ceases to operate. As a result, most commercially available centrifugal pumps are limited to comparatively low speeds and pressure per stage, such as a common type of submersible deep well water pump which may have as many as 15 stages, weigh as much as pounds, and have an overall length of five or more feet, whereas a comparative pump made in accordance with the present invention would require only two stages with the same overall diameter, an overall length of about seven inches, and weigh less than ten pounds.

Another object of the present invention is to provide a new and improved centrifugal liquid pump having means for creating an atmosphere of air or gas removed from the pumped liquid for surrounding the motor rotor.

It has been found in accordance with the present invention that a high speed motor operating at speeds of the order of 12,000 revolutions per minute such as contemplated, would have serious friction losses at the gap surface between the rotor and stator, if permitted to operate submerged in the liquid. Continued operation of such a motor for a prolonged time would result in a prohibitive loss in motor efiiciency and thus a serious loss in pumping efficiency. To fill the gap between the rotor and the stator with gas, the gas removed from the pumped liquid by the centrifuging action of the impellers is bubbled into the lower end of a sealed diving bell rotor compartment and thus displaces the liquid until said compartment is completely filled with gas.

Various other objects, features and advantages of the present invention will be apparent from the following description and from the accompanying drawings, in which FIG. 1 is a cut-away side elevation of a complete twostage pump embodying the present invention;

FIG. 2 is a transverse section of the pump along the lines 22 of FIG. 1 and shows a half-section of the first stage discharge diffuser and volutes, and a half-section of the first stage inlet passages comprising five inlet jets with five interstage crossover passages, shown in section, interspersedtherebetween;

FIG. 3 is a circumferential section of the pump taken along the lines 33 of FIG. 2;

FIG. 4 is a partially fragmented transverse section of the pump taken along the lines 4-4 of FIG. 1 and shows a half-section of the interstage passages between the. first and second stages and a fragmented half-section of the discharge volutes of the second stage fragmented to show the overbends in the elbows at the volute discharges of the last stage;

FIG. 5- is an enlargement of the injector section shown in FIG. 1 but shown in connection with the detailed illustration of the air or gas removal; and

FIG. 6 is a fragmented transverse motor end view of the pump shown in FIG. 1.

Referring to the drawings, there is shown a two stage, vertically suspended, submersible pump 10 for pumping water, oils, chemicals and the like, although as far as certain aspects and features of the invention are concerned, the pump may with minor variations have any number of stages to obtain any desired final discharge pressure, and; may be employed to compress or otherwise pump gases. The pump 10 comprises a motor casing 11 containing a motor stator 12 and a rotor 13. The rotor 13 is rigidly secured to a hollow rotatable shaft 14 on which are keyed or otherwise afiixed a first stage impeller 15 and a second stage impeller 16. The pump 10 also comprises a pump casing 17 made up, of three substantially circular members supported on one such member and comprising a first stage back plate member 20, an intermediate member 21 and a discharge member 22 threaded for connection to a discharge pipe (not shown) which may optionally contain a check valve and be connected to a tank with the other common accessories normally used in a complete pump system. The motor casing 11 and the back plate member are affixed to the intermediate member 21' by cap screws 23 and the discharge member 22 is likewise aflixed to said intermediate member 21 by cap screws 24.

Motor leads 25 pass through holes inmembers 20, 21 and 22 and are sealed pressure tight (not shown) in the wall of motor casing 11-. The intermediate member 21 isshown provided with a plurality of equally spaced inlet openings 26. for the first stage impeller 15, five being shown covered by a circular sand screen 27. Where the leads 25 pass across one of the inlet openings 26, they are protected from damage and abrasion by metallic tubes 28 inserted into member 21.

The motor stator 12 contains windings 30 encapsulated in. a resinous material 31' such as Epon resin a trade name for a resin possessing terminal epoxide groups, or a suitable silicone encapsulating compound, and the rotor 13 is separated from the stator by a sleeve 33 of stainless steel; or other suitable material and sealed liquid-tight by O-ring seals 34. The hollow shaft 14 carrying the rotor 13 is rotatable on a unit bearing sleeve 35, which has a thrust flange 36 and which is rigidly mounted on a'fixed hollow spindle 37 mounted rigidly to a motor end bell 38- by a nut 39. The lower end of the fixed spindle 3 7 has a down thrust flange 40 to carry the small unbalanced weight of the rotor parts as well as any small unbalance of pressure between the stages through its seating contact with thethrust flange 36 on the bearing sleeve 35-. On the upper end of the rotatable shaft 14 is a female cone center 41 separated by a space clearance 42 from corresponding fixed male cone center 43 secured to the discharge casing member 22, to limit upward travel 4,, of said shaft during starting, stopping or, handling of the pump.

Mounted tightly in back plate 20 is shaft seal 44 of well known construction, serving the dual purpose of preventing substantial leakage of liquid from the discharge of the first stage impeller 15 into a motor rotor compartment 45 during operation and corresponding substantial leakage of trapped air or gas from said compartment, when the pump is not operating. The seal 44 also serves to exclude sand or foreign particles from the compartment 45 and in this function is aided by a sand shield 46 and radial vane sand slingers 47 on the back of the impeller 15.

At the bottom end of the pump 10 and mounted on the end bell 38 is a flexible bellows 50, soldered or otherwise sealed to a ring 52 and sealably closed at one-end by a disc 51. The enclosure within the bellows 50 is connected by passage 53 between the ring 52 and the disc 51 and by a passage 54 in end bell 38 to a stator compartment 55, sealed against leakage by an O-ring 56. The bellows 50 is filled with a common type transformer insulating liquid 57, such as is commonly sold under the trade name Pyranol, one of the askarel compounds. The bellows 50 is protected from injury by a vented cap 58 secured to the end bell 38 by screw studs 59. The hydrostatic pressure on the bellows 50 serves through the medium of the insulting material 57 therein to equalize the pressure inside and outside the stator compartment 55 irrespective of the depth of submersion of the pump or temperature expansions or contractions, thus preventing leaks of the pumped liquid around the seals 34 from coming in contact with the electrical stator windings 30 or preventing the outward leakage of the insulating fluid 57.

The intermediate member 21 is provided with a plurality of equal radial entrance passages 26 (FIG. 2) for the first stage impeller 15, five being shown equally spaced. Although the five inlet passages 26 are shown for forming a corresponding number of jets for admission to the eye of the first stage impeller 15', any number of these passages may be provided within a practical range, as long as these passages are circumferentially distributed so that the resultant of the radial jet momentum (inlet jet velocity Xmass) on one side of any selected radial plane passing through the impeller axis is substantially equal to and in substantially radial alignment with the resultant of the radial jet momentum on the other side of the plane. For that purpose, the number of inlet passages 26 may be even and these may be arranged in diametrical. pairs in a manner similar to that indicated in the aforesaid Patent 2,868,440 or may be odd and these passages may be equally spaced or may be otherwise spaced. to attain balance in jet momentum in a manner similar to that indicated in the aforesaid application Serial No. 175,940.

The entrance passages 26 have comparatively large respective areas at their outer peripheries where the fluid, passes through the protective sand screen 27 and converge towards and into round edged respective orifices. 60, thus producing equally spaced equal jets directed radially inwardly toward the entrance eye 61 of the first impeller stage impeller 15.

The impeller 15 comprises a plurality of circumferentially spaced blades 62, so shaped, that they are concave,

on their leading faces and are generally forwardly curved at their outer peripheries or discharge ends as respect to their direction of rotation, and have, respective inlet portions 63 inclined outwardly and forwardly to efficiently receive the flow from entrance eye 61 in a shock-free manner. Around impeller 15 is a firs-t stage radial diffuser 64 serving to convert velocity head, to pressure head and around this diffuser are a plurality of similar perimetric involute discharge scrolls 65, five being shown, equally spaced and of equal size and conformation, for gathering the fluid from the diffuser and forcing it therethrough by its rotation, the fluid from each scroll being discharged through an elbow 66 and through a crossover passage 67. to the'next stage. The number of scrolls and their spacing may vary as long as they fulfill the requirements of balanced momentum set forth in the aforesaid application and patent.

The casing 17 is substantially circular and the discharge involutes 65 follow somewhat the circular contour of the casing and terminate in overextended outlet elbows 66 respectively equally spaced around the inside of said casing. The discharge involutes 65 have respective crosssectional areas expanding towards their respective elbows 66 and serve thereby not only as discharge conduits but also as diffusers to further convert velocity head to pressure head.

As fluid goes through an elbow it tends to crowd towards the outer bend of the elbow and away from the inner bend due to centrifugal action, so that the resultant momentum of the jet, i.e. the jet velocity times its mass, is offset from the positional center line of the jet passage at the outlet of the elbow. This adverse condition is substantially nullified by shaping each elbow 66, so that the momentum of the elements of each jet emerging fro-m the elbow is substantially uniform across the elbow from the inner bend to the outer bend. For that purpose, the inher bend on the upstream side of the elbow 66 from which the stream tends to break away as it flows through said elbow, turns through an angle only sufficiently to direct the stream from the scroll or volute 65 .along the passage 67 but the outer bend at the downstream side of the elbow has an overbend, i.e. turns through an angle greater than that sufficient to direct the stream in the direction of the passage. The effect of this overbend in the elbow 66 is to compensate for the tendency of the stream to crowd towards the outer bend and to cause thereby the resultant momentum of the jet entering the passage 67 to be almost coincident with the center line of the passage. The function of the overbend elbow 66 is described in detail in the aforesaid copending application.

Another aid in preventing the stream passing through the elbow 66 from breaking away from the inner bend of the elbow is a protuberance 68 on the upstream portion of said bend to deflect the approach stream away from the immediate area of the bend to crowd said stream around and over such protuberance into the sides of the passage 67 and thereby increase the actual and effective radius of the inner bend. The function of this protuberance 68 is also described in detail in the aforesaid application.

Each of the crossover passages 67 terminates in an overbend elbow 70 (FIGS. 1 and 4) for directing the fluid streams from an axial direction in passage 67 to a radially inward direction toward and in radial alignment with the eye of the second stage. The outer bend of the elbow 70 is overextended to cause the resultant momentum of the .jet emerging radially from said elbow to be almost coincident with the center line of the passage and to pass through the axis of the eye of the second stage, and the inner bend has a protuberance to maintain a constant bend area to 'aid further in preventing the stream from breaking away from the inner bend, in the manner described in the aforesaid copending application.

The termination of the overbend elbows 70 produces a plurality of equally spaced radially inward jets, five being shown of balanced equal magnitude coursing towards the eye 71 of the second stage impeller 16. The blading of this impeller 16 is in every way similar to that of impeller 15, except that it is of opposite hand to permit face to face operation of the impellers and 16 on shaft 14.

The radial diffuser 64a and the involute discharge scrolls 65a of the second stage are likewise similar to the radial diffuser 64 and the involute discharge scrolls 65 of the first stage. These scrolls 65a have respective discharge elbows 66a with overextended outer bends and with protuberances 68a on their inner bends serving the functions of the overextended outer bends and protruding inner bends of the elbows 66 and 70 described above.

The overbend elbows 66a discharge in radially inward directions without the necessity of axial passages and additional elbows similar to the axial crossover passages 67 and elbows 70 at the outlet of the first stage, and direct the fluid from said elbows as five equally spaced radial jets of equal magnitude towards a pump discharge axial eye 72 and thence through a pump discharge pipe (not shown).

Although the specific embodiment of the invention is shown in connection with a liquid pump of the submers- =ible type, it should be understood that said pump, with minor adjustments for differences in physical properties, will ope-rate equally well in and with any fluid, such as gas or liquid, and that the broader concepts of the invention so far described, apply to all types of fluid pumps, including those normally referred to as blowers or compressors.

Where the pumped fluid is a liquid containing absorbed or entrained air or gas, the said air or gas will be centrifuged out of the liquid and will collect as a bubble near the hub or center of the impellers. To remove such air bubbles and to create at the same time a source of air or other gas for maintaining an atmosphere of such air or other gas around the motor rotor 13 and in the gap between the stator sleeve 33 and the rotor periphery at all sustained operating conditions, there is provided a small injector type pump 79 (FIGS. 1 and 5), built into the rotary shaft 14 and employing as motive power a small amount of the pumped liquid. This pump 79 comprises the fixed spindle 37 having on its upper end a tapered axial rod-like extension 80 extending inside and along a bore 89 of the rotary shaft 14 and rounded at its upper end. This spindle extension 80 defines with the encompassing shaft 14 the inner wall of a venturi throat 81 and a diffuser 82. The shaft. 14 has a row of holes 83 at the throat 81 communicating with an annular recess 84 connecting into a series of holes 85 in the hub of the impeller 15 leading from the radially inner side of the entrance eye 61 of the impeller. Also located on the hub surface of the impeller 15 and on a spacer sleeve 86 arranged between the hub of the impeller 15 and the hub of theimpeller 16 are radial ribs 87, which aid in separating the air or gas from the liquid and which also serve as sand slingers to prevent small sand or gritty particles from entering the injector pump 79 and thence finding their way to the bearing of the shaft 14. Similar radial ribs 87a are also connected to the hub surface of the impeller 16 and on a spacer sleeve 86a located between the hub of the impeller 15 and the hub of the impeller 16 to serve as sand slingers.

During pump operations, the air or gas is separated from the liquid being pumped by centripetal action and collected in the form of a bubble 88 in the first stage at the hub of impeller 15 and to a lesser extent in the form of a bubble 88:: at the hub of the impeller 16. A small quantity of the pumped liquid passes down the bore 89 of the shaft .14 and through the throat 81 and by its injector or aspirating action draws the air or other gas from the bbuble 88 and discharges the mixture of liquid and air or other gas through holes 90 in the fixed spindle 37 at the base of the rod-like spindle extension 80, into an axial bore 91 of said spindle and to the bottom of the motor. Air bubble 88a at the hub of the impeller 16 is forced by the full pressure of the first stage through a clearance space 92 between the axial bore of member 21 and spacer sleeves 86a and 86 and add to the bubble 88 which in turn is removed in the manner described.

The combined air or other gas and liquid discharge from the injector diffuser '82 due to the centrifuging action of the rotating shaft 14 again separates and forms another bubble 98 around the small section of extension 80 and serves a dual purpose of supplying relatively gas free liquid to the upper end 93 of unit bearing sleeve 35 for lubrication and cooling and of supplying air or gas for the motor rotor compartment 45. The remaining 7 mixture over and above that required for the bearing sleeve 35 passes out from the bottom end 94 (FIG. 1) of the fixed spindle 37 in the form of liquid and entrained bubbles and into a chamber 89. The bubbles strike a gauze screen 95 in the chamber 89 across the discharge end of the spindle 37 and are deflected upward through holes 96 in the end bell 38 to the motor rotor compartment 45. The liquid passes freely through the screen 95 and out through radial slots 97 ('FIG. 6) in the end bell 38 extending from the chamber 89 below the screen to the surrounding well or reservoir. When the motor rotor compartment 45 becomes completely filled with air or gas, the liquid level in the chamber 89 drops to the point where the active part of the gauze screen 95 is exposed above said level, so that liquid and gas will then pass freely through said screen for discharge through the radial slots 97. The rotor'compartment 45 is thereby maintained with an atmosphere of air or gas, which serves to prevent excessive loading of the motor.

For applications where the pumped liquid contains little or no absorbed or entrained air or gas, as for instance in a boiler feed water system where special apparatus is employed to remove all such gases, the injector type pump 79 may be eliminated and a well known type of high pressure shaft seal and an external driving means such as a high speed turbine may be substituted without affecting the thrust balancing and other important features of the present pump or the broad concepts of the invention.

While the invention has been described with particular reference to a specific embodiment, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. A centrifugal liquid pump having an impeller and a hub for said impeller, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, and pump means separate from said impeller and responsive to motive power supplied by the liquid pumped for drawing the gases collected near said hub away from said hub, independently of gravity action.

2. A centrifugal liquid pump having an impeller, a hub for said impeller and a hollow shaft for driving said impeller, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, and pump means separate from said impeller and operable in response to the rotation of said shaft for drawing the gases collected near said hub and conducting them through the hollow of said shaft away from said hub independently of gravity action.

3. A centrifugal liquid pump having an impeller and a hub for said impeller, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, and aspirating means for pumping the gases collected near said hub away from said hub, and comprising a hollow tube coaxial with the impeller and having communication with the interior of said pump for causing some of said liquid to be conducted along said tube, said tube having communication with the region near said hub where said gases are collected to cause the collected gases to be injected into said tube by aspiration.

4. A centrifugal liquid pump having an impeller, a hub for said impeller and a hollow shaft for driving said impeller, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, means for conducting part of the pumped liquid along said shaft, and a fixed spindle having a tapered axial rod-like extension extending inside and along the hollow of the shaft, said spindle extension defining with the encompassing shaft the inner Wall of a venturi throat and a diffuser, said shaft having holes extending from near the hub where the gases collect to said throat, whereby the gases are drawn by aspirating action into 8 I said shaft to'be carried away by the liquid passing through said shaft.

5. A centrifugal liquid pump having an impeller, a hub for said impeller, a hollow shaft for driving said impeller, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, means for conducting part of the pumped liquid inside and along said shaft, means for drawing the gases collected near said hub into the liquid in said hollow shaft for entrainment therein, a motor for driving said shaft comprising a rotor connected to said shaft and a bearing for said shaft, means responsive to the rotation of said shaft for separating the gases entrained in the liquid from the liquid in said shaft and for collecting theseparated liquid in a region of said shaft, and means establishing communication between said bearing and the region of said shaft, whereby the separated liquid in said shaft lubricates said bearing.

6. A centrifugal liquid pump having a pump casing, an impeller, a hub for said impeller, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, a motor casing forming a unit with said pump casing and defining a rotor compartment, a motor in said motor casing comprising a stator secured to said motor casing, a rotor in said rotor compartment for driving said impeller, and means for drawing the collected gases near said hub away from said hub and for conducting them substantially free of the liquid into said rotor compartment to prevent excessive motor frictional losses.

7. A centrifugal liquid pump having a pump casing, an impeller, a hub for said impeller, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, a motor casing forming a unit with said pump casing and defining a rotor compartment, a motor in said motor casing comprising a stator secured to said motor casing and a rotor in said rotor compartment for driving said impeller, means for diverting part of the liquid in the form of a stream, means for drawing the collected gases near said hub away from said hub and'for entraining them in said diverted stream, means for separating the gases entrained in said stream from the liquid in said stream, means for conducting the separated gases into said rotor compartment to prevent prolonged overloading of said motor, and means for discharging the liquid from said stream to the outside of the pump.

3. A centrifugal liquid pump as described in claim 7, said separating means comprising a chamber for collecting the liquid from said stream before being discharged to the outside of the pump, a screen in said chamber, and a passageway between said chamber and said rotor compartment, said screen extending in said chamber across the flow of the stream into said chamber, whereby the gases in the stream are deflected from said screen into said passageway as said stream strikes said screen.

9. A centrifugal liquid pum-p comprising a pump casing, an impeller in said casing, a hollow shaft connected to said impeller for driving said impeller, a motor casing forming a unit with said pump casing, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, means for drawing the collected gases from near said hub and conducting them to and along said shaft, and means for diverting said gases substantially free of liquid from said shaft to the interior of said motor casing to prevent prolonged overloading of said motor.

10. A submersible centrifugal liquid pump adapted to be submerged in the liquid to be pumped and to be held with its axis of rotation in upright position for pumping action, comprising a pump casing, an impeller in said casing, an axial discharge passageway for the liquid pump at the upper end of said pump casing, a hollow shaft connected to said impeller and adapted to be supported in upright position for operation, said shaft having communication at its upper end with said discharge passageway whereby part of the pumped liquid isv diverted .to said hollow shaft for downward flow therein, a motor casing below the pump casing forming a unit therewith, the gases entrained in the liquid being separated from the liquid and being collected near said hub by centripetal action, means for drawing the collected gases from near said hub and entraining them in the liquid in said shaft for conduction therewith downwardly along said shaft, means at the lower end of said shaft for separating the gases from the entraining liquid, and means for diverting the separated gases into said motor casing to prevent prolonged overloading of said motor.

11. A centrifugal liquid pump comprising a plurality of coaxial stages, each of said stages including an impeller and a hub for said impeller, a hollow shaft for driving said impellers, the gases entrained in the liquid being separated from the liquid and being collected near said hubs by centripetal action, means for conducting part of the pumped liquid inside and along said shaft,

means for drawing the gases collected near said hubs into the liquid in said hollow shaft for entrainment therein by the aspirating action of the liquid conducted along said shaft, a motor for driving said shaft comprising a rotor connected to said shaft and a bearing for said shaft, and means establishing communication between said bearing and the hollow of said shaft, whereby the liquid in said shaft lubricates said bearing.

References Cited by the Examiner UNITED STATES PATENTS 1,143,957 6/15 Hansen 103-113 FOREIGN PATENTS 416,173 9/34 Great Britain. 588,102 5/47 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

ROBERT M. WALKER, Examiner. 

1. A CENTRIFUGAL LIQUID PUMP HAVING AN IMPELLER AND A HUB FOR SAID IMPELLER, THE GASES ENTRAINED IN THE LIQUID BEING SEPARATED FROM THE LIQUID AND BEING COLLECTED NEAR SAID HUB BY CENTRIPETAL ACTION, AND PUMP MEANS SEPARATE FROM SAID IMPELLER AND RESPONSIVE TO MOTIVE POWER SUPPLIED BY THE LIQUID PUMPED FOR DRAWING THE GASES COLLECTED 